1. Field of the Invention
This invention relates to a method for minor actinide nuclides incineration by burning them with minimized effects from rare earth elements.
2. Description of the Related Art
Spent fuel in a light-water reactor contains minor actinide nuclides with long half-lives. Use of a fast reactor for the minor actinide nuclides incineration is currently being studied. To do this, the minor actinide nuclides need to be separated and extracted from the spent fuel. In the nuclide separation technique, neptunium (Np) of the minor actinide nuclides can be easily separated from the spent fuel by a Purex process. Americium (Am) and curium (Cm) can be separated by a Truex process. However, since americium and curium exhibit almost the same behavior as rare earth elements, when americium and curium are separated from the spent fuel, rare earth elements are also extracted at the same time.
FIG. 1 is an illustration showing the percentage of nuclides taken out in each process of spent fuel reprocessing. The Purex process and the Truex process may be combined to provide a method of separating minor actinide nuclides from light-water reactor spent fuel. In this method, plutonium (Pu), neptunium (Np), and uranium (U) are extracted with the Purex process and americium (Am), curium (Cm), and a large amount of rare earth elements are extracted with the Truex process. Thus, when minor actinide nuclides are added to reactor core fuel to make them incinerate, rare earth elements are inevitably mixed at the same time.
However, the rare earth elements exist in large quantities (ten times or more) compared with americium and curium, and are large in neutron absorption; if a reasonable amount of americium and curium extracted from spent fuel is added to the reactor core for americium and curium incineration, because of the neutron absorption of the rare earth elements, the reactivity required for burning becomes large, leading to difficult operation control of the fast reactor.